Some helpers (eg. ftp) assume that private area in conntrack is
filled with zero. It should be cleared when helper is changed.
Signed-off-by: Yasuyuki Kozakai <yasuyuki.kozakai@toshiba.co.jp> Signed-off-by: Patrick McHardy <kaber@trash.net> Signed-off-by: David S. Miller <davem@davemloft.net>